Field of the Invention
This invention relates in general to a device and method for acoustic sensing, and in particular to a device and method for acoustic sensing using a multi-fiber optical probe.
Description of the Related Art
Most acoustic sensor applications requiring directional acoustic source information employ processing of signals received on spatial arrays of omnidirectional pressure sensors. Acoustic vector sensors—defined as a sensor able to measure both pressure and particle motion (e.g., displacement, velocity, or acceleration)—offer a number of advantages including comparable directivity with a physically smaller array, as well as some degree of directional information using only a single sensor. Further, directivity gains can be achieved even when single axis vice tri-axial vector sensors are employed.
Typically, an acoustic vector sensor is realized by using two co-located sensors, such as piezo-electric transducers (“PZTs”), one a monopole or omnidirectional dynamic pressure sensor and the other a dipole or directional sensor. The latter is usually obtained by exploiting one of two principles: (1) inertial sensing involving displacement, velocity, or acceleration or (2) pressure gradient detection. In all cases, sensor directionality is achieved because of the vector nature of each of these quantities. Examples of such devices include vector sensors whose directional component uses piezoelectric accelerometers and particle velocity sensors, which uses a moving coil. Examples of more specialized devices include sensors that sense the pressure gradient or acoustic flow.
Typically, the advantages associated with deploying directional sensors are enhanced if the device is small and robust and consumes comparatively little power. Low power is especially important in certain underwater applications, where one desires operation over a long time period but regular access to the deployed sensors might not be possible. For applications in air, the lack of sensitivity to electromagnetic interference (“EMI”) can also be important. Finally, some applications require very low frequency (e.g., sub-Hertz) performance, which can be difficult to achieve with piezo-based approaches because of the significant increase in electrical self-noise at these very low frequencies.